Arc lamp control



Nov. 22, 1949 B. HOPKINS ETAL ARC LAMP CONTROL 2 Sheets-Sheet 1 Filed Nov. 18, 1946 INVENTORJ, BEN baPm vs and P/u PH R. 74 5055,

Nov. 22, 1949 B. HOPKINS ET AL 2,439,137

ARC LAMP CONTROL Filed Nov. 18, 1946 2 Sheets-Sheet? Pam/1 b. [168.05,

HTI'OEIYEYS.

Patented Nov. 22, 1949 STATES PAT ENTT OFFICE ARC LAMP CONTROL B'enzHopkins, Indianapolis, and Ralph A. Woods; Morgantown, Ind.

Application November 18, 1946, Serial No. 710,426"

Claims.

This application relates" to" electric arc" lamps, especially to electrode feeding mechanism for such lamps-.-

Lamps of" the" type to which" this invention relates are=commonly used formotion picture projection. In them, positive and negative carbon electrodesare fedtowardeach other, usually from oppositedirectionsa-long the axis of an elliptical reflector, to provide a' continuous arc at or about the focalpoint'of the reflector. To maintain the continuousarcof the desiredcharacteristics at the desired point, the two electrodes must be fed'accurately toward the are at different rates proportional totheir difi'erent rates of consumpt-ion. Commonly, the negative carbon is supported, and-fed, through an opening in the center ofth'e reflector; and the positive carbon is-ied-by an arm through a guide, both'ot which necessarily lie in the path of light.

The-electrodes areof carbon, often sheathed with a thin layer of conductive-metal. They are relatively fragile, yet they must'be'mechanically supported and=connected to an electrical circuit in' such a positive 'way that there is no arcing or" excessive voltage dropat the connections. They must be frequently-replaced'andmore frequently must'be-a'dvan'ced in their-holders if they areto be fully consumed. On each such occasion the holders" must be reset with respect to the driving mechanism;

Inprior lamps; the 'electrod'e holders impose considerable danger to the fragile carbon electrodes, both of crack-ingthe electrode itself and of breaking the metallic sheath 1 of the electrode. In addition, the operating" mechanism for the holders has been so arranged'with respect to the are that it was heated' excessively-- and was difficult and hazardousto use, as" for resetting electrodes, without" excessive delay to permit the whole lamp to cool;

Prior electrode holders have been driven at fixed relatlveirates; as by a -pair' of screws geared to give feeding ratesgenerally proportional to the consumption of the two electrodes: Such prior." drives arefldesignedito= use particular" and uniform sets: of: electrodes;v under particular and rigid COl'lditlOl'lSOf'CUlIIBiIt SUpDIY. Such drives are inflexible; and: usually requireconstant attentionand' adjustment by an operator, to compensate for variations? in" current Supp y and especially for the particular "characteristics of the current; supply, which 1is.-.availablein :a particular installation Without: such constant attention and .frequent manualadjustment; the variations from the-z conditions 1 for? which? thelamp was 2v specifically designed causethe arc to travel'from its desired point either toward'or away from the reflector, with consequent loss'in the quality of light produced.

It is the objectof our invention to provide improved electrode" supply mechanism for an' arc lamp; which will providea good electrica1.connection'between the" electrodes and theirholders with. substantially no danger of breaking or cracking the electrodes; which. will be adapted for ready and quick interchange and resetting of the "electrodes by means that is rem'oved'from the heat of the lamp; which' imposes a minimum" of obstruction in'the'light' path; which will'giveirnproved electrode feedingatproper relative speeds to maintain the arc-with the propercharacteristics and in theproper position, which'may be readily adjustable over-a range to-suit thepar ticular characteristics: of current available in particular installations and when so adjusted will truly maintain aproperarc-at the desired point without constant or frequent attention, and which will lend itself to ready conversionfor operation of the lamp-at different'intensities.

In a preferred form of our invention, we drive electrode carriages along parallel feed screws, continuously drive' oneof said screws by means responsive to the current acrossthe arc, and drive the second from that same source through an infinitely-variable; constant drive. On each electrode carriage we mountan electrode holder which provides for positivefeedof-its electrode toward the arc.

The negative electrode holder rises from its carriage'behind thereflector'and feeds its electrode through a centeropening in the reflector. The holder provides some-universal movement forthe electrode; and the forward endofthe electrode ispositionedby an adjustable guide which also extends through the reflector opening, The positive electrodeholder passes through a laterall open'slot in'the'fi'oorof'the lamp, then rises outside the light beam to-the level ofthe reflector axis. A radial arm extends inward at that level to hold the positive electrode on the reflector axis. The arc-end of the positive electrode is guided at the end ofan opposite radial arm extendinghorizontally inward from the oppositeside of'the reflector from the holder arm. The holder and guide arms are symmetrically arranged at about the level of the arc and are relatively thin; and they cause minimum disturbance to the light beam and absorb a minimum-amount of'heat;

Each electrode-is firmlygripped between members formed to engage its surface over substantial curved areas of its circumference and over a considerable axial distance, for example 2 to 4 times the diameter of the electrode, which gives an extensive area of engagement between each elec trode and its holder. The electrode gripping parts are at the ends of arms extending inwardly and are mechanically connected to be thrust toward each other by manual operation, to grip the electrodes with considerable pressure. The arrangement, involving a large gripping area on parts thrust toward each other, gives improved electric contact, permits the use of considerable pressure to enhance the electrical connection substantially without danger of damage to the electrodes, and holds the electrodes firmly throughout their operation. The gripping parts are operated manually by handles positioned at the remote ends of the supporting arms and outside the light beam, the negative electrode handle being behind the reflector, and the positive electrode handle being at the outer end of the radial holder arm; and we have found that our arrangement permits the electrode to be reset and replaced quickly and readily without unnecessary delays for cool ing and without danger of breakage.

The accompanying drawings illustrate my invention. In such drawings, Fig. 1 is a plan showing pertinent parts of an arc lamp embodying my invention; Fig. 2 is a side elevation of the structure shown in Fig. 1; Fig. 3 is an end elevation of structure shown in Fig. 1, with the base in section; Fig. 4 is a vertical longitudinal section of the negative electrode-holder; Fig. 5 is a horizontal section in the plane of the axis of the two electrode-driving screws; Figs. 6 and 7 respectively are end and top elevations of the driving connections between the two electrode-driving screws; and Fig. 8 is an enlarged plan of the gripping head of the positive-electrode holder.

The arc lamp structure shown in the drawing includes a base I8 which supports the housing and other usual parts of the lamp. It is desirably of inverted box form and houses the electrode driving mechanism below its top wall I5. A reflector II is mounted on the base I8 by usual means to provide adjustment for aligning its axis as desired. A negative electrode I2 extends through a central opening in the reflector, and a positive electrode I3 is positioned in alignment therewith to arc at the point I4 between the ends of the electrodes I2 and I3.

The electrode feeding mechanism includes a pair of shafts I8 and I9 journaled in the end walls of the base I8 and extending longitudinally thereof, parallel to the axis of the reflector I I. The shaft I8 is positioned below the axis of the reflector II and desirably slightly to one side thereof. It is threaded over approximately the rear two fifths of its length, and is used to drive the negative carbon I2. The shaft I9 is parallel to the shaft I8, conveniently in the same hori zontal plane, and spaced outwardly from the shaft I 8. It is threaded over approximately the front three fifths of its length, and is used to drive the positive carbon I3. The shafts I8 and I9 are drivingly interconnected by means which will be described, to rotate at speeds to give the desired proportional feeding rates of the two electrodes.

A carriage 28 for the negative electrode is slidably mounted on the two shafts I8 and I9 at the threaded end of the shaft I8. It carries a worm gear 2I on a horizontal axis below the shafts I8 and I9, in engagement with the threads of the 4 shaft I8. The shaft 23 of the gear 2| extends outward through a slot in the side wall I8 of the base I8, and carries an insulated handle 22 at its end. A friction brake 24 normally holds the shaft 23 against rotation with respect to the carriage 28, so that rotation of the shaft I8 causes longitudinal travel of the carriage 28. Manual operation of the handle 22 rotates the worm 2I against the friction brake, to adjust the carriage along the threads of the driving shaft I8.

From the carriage 28 a post 25 rises through a slot 26 in the top wall I5 of the base, to support the negative electrode holder. The holder comprises an inverted L-shaped member 21, the ver tical leg of which is loosely bolted against the side of the post 25, as by a pair of bolts 28 loosely received in holes 29 through the vertical leg of the member 2'1. The horizontal leg 38 of the member 27 is offset so that it overlies the end of the post 25. It extends forwardly, and at its forward end carries a depending boss 3|. The horizontal leg 38 is drilled to provide a longitudinal, inclined bore to receive a clamping slide 32, the rear end of which carries a rack 33 in engagement with a gear 34 manually operable by a handle 35. A hole longitudinally through the boss 3| forms a seat to engage the lower circumferential half of the negative carbon electrode I2; and the forward end of the slide 32 is shaped to engage the upper half of the electrode I2. The engaging surfaces, especially on the boss 3I, are desirably curved to mate with the surface of the electrode, and extend axially of the electrode I2 a considerable distance, for example 2 to 4 times the diameter of the electrode. The electrode I2 is clamped in place by operation of the handle 35 to cause the gear 34 to move the gripping slide 32 forwardly to wedge itself into gripping engagement with the electrode I2.

From the holder 3835, the negative electrode extends forward through an opening in the center of the reflector II, to the arcing point I4. Just short of its end at the arcing point I4 the electrode I2 rests in a notch 38 of an adjustable guide 39 which extends forwardly from a point of support through the central opening of the reflector II. The holder 38-35 supports the electrode I2 substantially on the axis of the reflector II, and the looseness of the connection between the vertical leg 21 of the electrode holder of the post 25 permits the electrode I2 to adjust itself to the position of the guide 39.

A carriage 48 for the positive electrode I3 is slidably received on the forward ends of the shafts I8 and I9. It is interconnected to the threads on the shaft I9 by a worm gear M on a shaft 42. Such shaft 42 extends horizontally below the shafts I8 and I9 and through a slot in the side wall I6 of the base, where it carries an operating handle 43. A friction brake 44 normally locks the gear 4I against rotation with respect to the carriage 48 so that rotation of the shaft I9 causes longitudinal travel of that carriage 48. As is best seen in Fig. 3, a post 45 for supporting the positive electrode rises from the carriage 48 first vertically, then horizontally inward beneath a shielding cover I1 forming part of the top wall I5 of the base I8, then outward and upward in a curve outside the path of light from the reflector. From the upper end of the post 45, an arm 48 extends inward to support the positive electrode I3 on the axis of the reflector. Such arm 46 is inclined to the axis of the reflector II, as may be seen in Fig. 1, so that it supports the electrode I3 at a point near its rear answer end; gwhichspermitsr-aagreater ,lengthzofztlieselecs trodezto.be.iedwithoutresettingstheholder; The arm; is intheeform :of, a: relatively; flatxbar, bent laterally at its end to extend at a right angle-'to theaxiszof the reflector. ItQiSLDOSitlOIIGdVwith a thin edger towardtheireflector, so Lthattit presents a r minimum obstruction in thezlightzbeamn At its. inner-:end; the arm 46: carries a stopv 48", and at1its outerrendaxlug 49;, A thrustimember 5|, desirablyiormed-fof'sheetxmetal bent :to loosely embrace the arm146,...is; slidablylmounted onzthe arrm between the1lug..'49:and:: the stop 48. The depending wall on then-reflectonside:ofzsaid meme ber 51 terminates-mean angular portion 53 which is normal to theireflector axis an'dirides against the: side' of; the parallel endlof. the.= arm. 46", to causez'the'forwardrend'ofthe member 51 to move at right-1' anglesto: the reflector axis a as it approachesgripping engagement with its electrode; Theinner endof them-emberil carriesa pressure member '52 to :moveztoward the stop 48 A thrust screw :BOJis threaded through the lug 49 and oper= atively connected to the thrust member 5'1, and is 'operatedtby atzh'andle 41 positioned beyond the OUtBIiJGlldI-Of-E the :arm .46; Desirably, the meeting faces of the members 482 and 52 are respectively shaped toipresentseating areaswhich fit the cylindrical. surface of thepositive electrode l3 over: both lazconsiderableaxial Eextent and a considerablecircumferential extent.

From the'holder, the. positive electrode extends toward the arcing point: [4, in alignment with the negativesel'ectrode l2. Just short of the end of the positive electrode l3;- it is guided'by engagementwithatguide surface on a'radial guide arm 55; supportedLfrom the opposite side of the lamp from theholder arm 45. Such guide-arm-55 is supportedon a' post 56 which is mounted on the base land-which extends upward and outward therefrom outside the path of light. The guide arm is relatively thimwhereitcuts the path of light'so that likeethe arm 46st presents a minimum obstruction in the pathof light; The two arms are generally v symmetricalland are positioned and shaped tocausea minimum disturbancein the light beam.

This arrangement permits operation. ofi the positive; electrode holder from a;-, relatively'cool point, so that it is readily possible'to resetior replace the positiveelectrode in the' holder'46"52 without waiting for the lampxtoucool; for the only part which needs to be touched is the operating handle 41 for the pressure screw 50 of that holder, and this handle 41 remains sufficiently cool during operation of the lamp so that no unnecessary wait is required when the arc is extinguished before that handle 41 may be operated manually to replace a positive electrode 13.

The electrode feed screws I8 and I9 are driven by a motor 60. This operates a gear 6| which meshes with a gear 62 mounted on the end of the screw l8. The screw I9 is constantly operated from the same source, conveniently from the gear 62, by an infinitely-variable positive driving train. As shown, this driving train includes an idler gear 63 carried by an arm 64 pivotally mounted on the shaft IS. The side faces of the idler gear 63 are beveled, and engage between opposed faces 65 of a pair of cones 66 and 51 on the shaft 19. The cone 6! is adjustable toward and from the cone 56 to vary the depth of engagement between the idler gear 63 and the conical faces 65, and thus to vary the driving ratio between the shafts I8 and H). The axis of the idler gear 63 is parallel to the shafts l8 and I9, and is spaced from the plane of the axes of those shafts; by a distance; which depends upon: the adjustment of the cone 6-] and; the depth'bfen: gagement between the idler 63 and the-conestBB and 61. The; idler 63 entersbetweemthecones 66 and Slinthedirection ofrotation of the gear 62 and at, an :angle with a line joining .the centers of the shafts [Band l9, so that-driving operation of the trainxtendsto force the idler:63 into firm engagement with the faces 65 of the cones 65 and 51: The weight of thearm 6'4 and of the idler 63'" The motorxfifl is electrically connected in'known" manner so that its operation is responsive 'to' thelength of arc gap between the electrodes,.and

; maintains such gap at the proper length, Upon installation of the machine, the cone 6'! is adjusted to give a speed ratio between the shafts J8 and-.19 so that theyyfeed theirurespectively, associatedelectrodes atthe proper relative: rates-:to cause the arc to remain at the desired point; This adjustment must bebytrial, to suit the particular. characteristics of the current supplied.- Usually; thecurrent supply is adjustable-as by changing taps on a rectifierto give approximately the characteristics for which the lamp is designed, butit isusually difficult and frequently impossible to obtain exactly, the desiredcurrent characteristics: by adjustment of the current-supply. Althoughthe: lamp will operateeven thoughthe current varies'quite; widely from that for-which the lamp isdesigned, the. arc will not remain in theproper position; but will walk or travel along the: axis offthereflector, by consuming one, or theotherJJofthe electrodescat too great arelative rate This walking is readily overcome by adjust:-

merit of thespeed ratio between, the shafts: I8 and 19'. If. the are; travels toward; therefiector; thezrelative speed of'the positive electrode isyreduced, by adjusting the cone 6'! toward the cone 66. to decrease:the depth of. engagement between the idlerv 63 and the faces '55. Conversely, if the arctravels away fromtthe reflector; the feeding rate of the positive electrode is increased, by adjusting the cone 61 away from the cone 66 to increase the depth of engagement between the idler 63 and the faces 65.

Our electrode feeding mechanism provides feeding rates for the two electrodes which are truly proportional to their respective rates of consumption under all normal conditions in any usual installation, and the arc will normally remain fixed in any desired point without attention or manual correction by the operator. The lamp may be readily adjusted for operation at higher intensity at higher amperage with larger electrodes, merely by readjusting the variable drive to the proportional rates of feed required for the new conditions.

In preparing the lamp for operation, the carriages 2! and ti! are retracted along their feed screws l8 and as by rotation of the handles 22 and 43, and electrodes I2 and I3 are inserted in their respective holders. The electrode i2 is inserted by operating the handle 35 to retract the clamping member 32, an electrode 12 being then readily inserted from the rear through the hole in the boss 3|, and the handle 35 is then turned to force the clamping member 32 forward to firmly clamp the electrode l2 and establish a firm mechanical and electrical connection between it and its holder. The electrode I3 is inserted by operating the handle 41 to retract the thrust member 5| and open the clamping members 48 and 52 of the positive-electrode holder. The electrode is then placed between the clampin members, and the thrust member 5| moved forward by the handle 41 to firmly grip the positive electrade I3.

Both electrodes are gripped over a large area by fitting surfaces, which permits the electrodes to be firmly gripped under considerable pressure, to give a good mechanical and electrical connection between them and their holders, without danger of breaking or cracking the electrodes. We have found that there is no danger of such break age within the limits of manual tightening of the gripping members 35 and 41, and that such manual tightening readily gives proper and ample mechanical and electrical connection for the electrodes.

We claim au our invention:

1. In an arc lamp, a pair of feed screws respectively connected to feed the negative and positive electrodes, an electric motor positively connected to drive one of said feed screws, an infinitely-variable constant driving train interconnecting the driven feed screw with the other feed screw.

2. In combination in an arc lamp, a pair of feed screws respectively connected to feed the positive and negative electrodes, an electric driving motor geared to one of said feed screws, a pair of cones mounted on the other feed screw and provided with opposed conical faces, an idler gear driven by the gear train to said driven feed screw, said idler gear being beveled at the edges of its side faces and bein positioned with said beveled surfaces in engagement between the conical faces of said cones, said idler gear entering between said cones in the direction of rotation of its driving gear, and means urging said idler gear into engagement with said cones, said cones being adjustable to vary the spacing between them whereby to vary the speed ratio between the two feed screws.

3. In an arc lamp, negitive-electrode feeding mechanism, independent positive-electrode feeding mechanism, means for positively drivin one of said feeding mechanisms, and an infinitely variable constant driving train interconnecting said other feeding mechanisms to said driving means.

4. In combination in an arc lamp, a base, a reflector mounted on said base, a negative-electrode feed screw in said base parallel to the axis of said reflector and below its axis, a positiveelectrode feed screw parallel to said first feed screw and spaced laterally therefrom toward one side of the base, a motor mounted on said base on the opposite side thereof from said positiveelectrode feed screw, a gear on said negative-electrode feed screw driven by said motor, a pair of cones on said positive-electrode feed screw aligned with said gear, said cones being formed to present opposed conical faces, an idler gear driven from said first gear and having beveled edges in driving engagement with the conical faces of said cones, said cones being adjustable to var the spacing between them whereby to vary the speed ratio between said two feed screws.

5. In an arc lamp, a pair of feed screws respectively connected to feed the negative and positive electrodes, means for continuously driving one of said feed screws, and an infinitely variable constant driving train to the other of said feed screws, comprising a, rotor having beveled edges, and a pair of coaxial cones relatively adjustable axially and with conical faces in driving engagement with the beveled edges of the rotor, the rotor and cones being movable toward each other whereby axial adjustment of the cones varies the depth of engagement between the cones and rotor to vary the ratio of said train and adjust the relative speeds of said two feed screws.

BEN HOPKINS. R. A. WOODS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 357,378 Fisher et a1. Feb. 8, 1887 1,101,629 Hall June 30, 1914 1,696,777 Meyer Dec. 25, 1928 2,165,183 Nickelsburg July 4, 1939 2,301,011 Breukert Nov. 3, 1942 

